A survey was made in 3205 children aged 6-17 years from the families of natives residing in the areas exposed to nuclear explosion (Group 1). A control group comprised 3200 children living under the similar climatogeographic and social conditions (Group 2). In Group 1 children circulatory diseases, lymphadenopathies, connective and bone tissue dysplasias come first in the structure of morbidity. There was an increase in respiratory diseases at the expense of long-ill children. The fact that lymphadenopathies and connective and bone tissue dysplasias are predominant and respiratory infection is persistent suggests that small-dose radiation has a negative impact on the above systems.